The present invention relates in general to a hybrid electrical circuit and, more particularly, to a hybrid electric circuit device for supplying electric power of a desirably controlled frequency to a load such as an electric motor, which is applicable, for example, to a frequency conversion circuit.
The present invention also relates to a frequency conversion circuit, and is particularly concerned with an output circuit thereof.
Generally, a prior art frequency conversion circuit is known as disclosed in Japanese Patent Publication No. 62-42472, published Sept. 8, 1987. The circuit described in the aforementioned publication includes circuit switching elements for changing the direction in which a pulsating current is carried, each constituting thyristor elements, whereby a desired frequency is obtained from controlling an ignition timing of the thyristors.
Such prior art comprises a single thyristor module containing a plurality of thyristors for directly controlling power principally, a single diode module containing a plurality of diodes for rectification, a drive circuit for the thyristors, and an ignition timing control circuit of thyristors.
Since an ON/OFF characteristic of the thyristor is utilized, the prior art has a characteristic that the circuit automatically becomes off at the zero cross time of an impressed pulsating current. Accordingly, the direction of an electrical current to the load is changed generally at the zero cross point, a frequency of the alternating current generated from the frequency conversion circuit becomes one of the integral number of a frequency of the utilized AC power, and thus a continuity at the time of frequency variation is not satisfactory, an abnormal vibration arises on a load, or the load gets locked otherwise.
Meanwhile, in the case where the frequency conversion circuit is constituted of transistor elements, an arbitrary frequency can be generated, however, an ON/OFF control circuit and an independent power source for control will be necessary at every transistor element, and thus the circuit becomes inevitably large in size and complicated at the same time, and the thyristor module and the diode module are connected by a lead wire or wiring pattern. Accordingly, a pulsating current of large power flows to the lead wire or wiring pattern, and an significant electromagnetic noise is radiated from the lead wire or wiring pattern, thus causing a noise interruption in a TV, audio equipment and other such devices. Then, since the thyristor module and the diode module are separated from each other, the circuit size becomes large, and a troublefree a low cost operation is therefore not realized for the circuit.